Circuit board, electronic device and method for manufacturing the same

ABSTRACT

A circuit board includes a substrate, a circuit pattern and a through electrode. The circuit pattern is disposed on one side of the substrate in a thickness direction thereof. The through electrode is filled in a through-hole formed in the substrate with one end connected to the circuit pattern. The circuit pattern and the through electrode each have an area containing a noble metal component (e.g., Au component) and are connected to each other therethrough.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of application Ser. No.12/180,831 filed Jul. 28, 2008, which claims the benefit of priorityfrom prior Japanese Application Nos. 2008-128462 filed May 15, 2008 and2007-209696 filed Aug. 10, 2007, respectively. Further, the entirecontents of application Ser. No. 12/180,831 is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a circuit board, an electronic deviceand a method for manufacturing the same.

2. Description of the Related Art

Examples of electronic device include various scales of integratedcircuits and various types of semiconductor devices and chips thereof.

As means for realizing a three-dimensional circuit configuration inelectronic devices of this type, there has been adopted a method thatLSIs are disposed on a circuit board with multilayered wiringtherebetween. However, this method increases the mounting area with thenumber of LSIs, so that the signal delay between LSIs increases becauseof an increase in wiring length.

Accordingly, there has been proposed a technology of using a circuitboard with a circuit pattern disposed on one side and through electrodespassing therethrough in a thickness direction and connected to thecircuit pattern.

As one example of such circuit boards, Japanese Unexamined PatentApplication Publication No. 11-298138 discloses a process of filling anadhesive liquid material into through-holes or non-through-holes of amultilayered circuit board, wherein after the adhesive liquid materialis screen-printed on the circuit board under an vacuum atmosphere,differential-pressure filling is performed by reducing the vacuum degreeof the vacuum atmosphere or changing the vacuum atmosphere to a normalatmosphere.

In addition, Japanese Unexamined Patent Application Publication No.2000-228410 discloses a process of forming through electrodes, whereinthrough-holes of a high-aspect ratio are formed in a circuit board by anoptical excitation electropolishing method, an oxide film as aninsulating layer is formed by oxidizing the inner wall of thethrough-holes, and then the through-holes are filled with a metal by amelted metal refilling process.

Japanese Unexamined Patent Application Publication No. 2002-158191discloses a process of filling a metal into micropores through adifference in an ambient pressure, while Japanese Unexamined PatentApplication Publication No. 2003-257891 discloses a process of filling aconductive paste into micropores. Moreover, Japanese Unexamined PatentApplication Publication No. 2006-111896 discloses a process of formingthrough electrodes, wherein a metal is directly embedded intothrough-holes before and after a plate embedding stage.

As means for realizing a structure in which through electrodes areconnected to a circuit pattern in electronic devices of the type, thereare two main types of method. The first method is to previously formthrough electrodes, which contain Sn (tin) as a main component, on acircuit board and then form a circuit pattern. The second method is topreviously form a circuit pattern on a circuit board, perforatethrough-holes in the circuit board at locations corresponding to thecircuit pattern, and then filling a molten metal material such as Sn(tin) into the through-holes for formation of through electrodes.

The circuit pattern is formed by using a thin-film formation techniquesuch as CVD (Chemical Vapor Deposition) or sputtering. Such thin-filmformation techniques expose the circuit board to a high temperature.When using the first method, accordingly, the through electrodescontaining Sn as a main component melt in the thin-film formationprocess.

When using the second method, on the other hand, since the throughelectrodes are formed after formation of the circuit pattern, theproblem of melting of the through electrodes in the first method can beavoided. The second method is superior to the first method in thatpoint.

However, although the process of forming the circuit pattern on one sideof the circuit board is carried out under a vacuum atmosphere, thecircuit board is taken out into the air in the following processes offorming the through-holes and filling the molten metal materialthereinto. This results in oxidizing the surface of the circuit patternat the inner bottom surface of the through-holes.

Oxidation of the surface of the circuit pattern to be connected to thethrough electrodes deteriorates the connection between the circuitpattern and the through electrodes, thereby causing serious problemsthat cannot be overlooked in electronic devices of this type, such asinsufficient properties and a decrease in yield.

As means for solving the oxidation problem, there has been known atechnique of reducing the oxide film of the circuit pattern by using thereduction action of a flux.

However, the above reduction technique using a flux causes the followingserious problem. In detail, filling the flux into the through-holesalong with the molten metal material generates a flux gas. In electronicdevices of this type, the through-holes are micropores having a diameterof, for example, several tens of μm and a significantly high aspectratio. If a flux gas is generated in such through-holes, the escape ofgas inevitably becomes difficult, producing voids due to the flux gasaround the through electrodes, which leads to a decrease incross-sectional area of the through electrodes, an increase inelectrical resistance, poor connection to the circuit pattern, and anincrease in bond resistance.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a circuit boardsuppressing formation of an oxide film on a surface of a circuitpattern, an electronic device, and a method for manufacturing the same.

It is another object of the present invention to provide a circuit boardsuppressing formation of voids within a through-hole, an electronicdevice, and a method for manufacturing the same.

In order to achieve at least one of the above objects, the presentinvention provides a circuit board comprising a substrate, a circuitpattern, and a through electrode. The circuit pattern is disposed on oneside of the substrate in a thickness direction thereof, and the throughelectrode is filled in a through-hole formed in the substrate with oneend connected to the circuit pattern. The circuit pattern and thethrough electrode each have an area containing a noble metal componentand are connected to each other therethrough.

The circuit board according to the present invention may be combinedwith a circuit functional part to provide an electronic device.

When manufacturing the circuit board according to the present invention,at first, a substrate with a circuit pattern on one side thereof isprepared. Then, a through-hole is perforated in the substrate at alocation corresponding to the circuit pattern, wherein the through-holeextends from the other side of the substrate to the circuit pattern.Then, metal particles are supplied into the through-hole, wherein themetal particles have a noble metal disposed at least on a surfacethereof. Then, a molten metal material is filled into the through-holeto form a through electrode.

According to the above manufacturing method, even if the surface of thecircuit pattern is oxidized at the bottom of the through-hole, the metalparticles with a noble metal appearing on their surface can be melted bya melting heat energy at the step of filling a molten metal materialinto the through-hole for formation of the through electrode, therebythermally diffusing into the circuit pattern and the through electrode.As a result, the circuit pattern and the through electrode each have anarea where a noble metal component is dispersed in its composition andare connected to each other through the noble metal component-dispersedareas.

Noble metal materials generally have a higher melting point thanmaterials of the through electrode, but the melting point can besignificantly lowered by reducing the particles to a nano-size, allowingthe noble metal materials to be melted by a heat transferred from themolten materials of the through electrode.

The oxide film, which has been produced on the surface of the circuitpattern at the bottom of the through-hole before filling the moltenmetal material of the through electrode, can be reduced by catalysis ofthe noble metal particles. Thus, since the reduction does not need anyflux, formation of voids due to a flux gas can be avoided.

As another aspect of the present invention, the through electrode maycontain bismuth (Bi), gallium (Ga) and antimony (Sb). In the case ofcontaining bismuth (Bi), gallium (Ga) and antimony (Sb), it is possibleto eliminate voids from the resulting through electrode by using theircubical expansion properties.

As further aspect of the present invention, the through electrode maycontain a magnetic component such as iron (Fe), cobalt (Co), nickel (Ni)and alloys thereof. With these magnetic components, there may be adopteda filling method using a magnetic force in a filling process forformation of the through electrode.

The present invention will be more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically showing a structure of acircuit board according to one embodiment of the present invention;

FIG. 2 is a sectional view schematically showing another structure of acircuit board according to one embodiment of the present invention;

FIG. 3 is a sectional view schematically showing still another structureof a circuit board according to one embodiment of the present invention;

FIG. 4 is a sectional view schematically showing yet another structureof a circuit board according to one embodiment of the present invention;

FIG. 5 is a sectional view schematically showing yet another structureof a circuit board according to one embodiment of the present invention;

FIG. 6 is a SEM (Scanning Electron Microscope) photograph of aconventional circuit board as a comparative example;

FIG. 7 is an enlarged SEM photograph of FIG. 6;

FIG. 8 is a SEM photograph of a circuit board according to oneembodiment of the present invention;

FIG. 9 is an enlarged SEM photograph of FIG. 8;

FIG. 10 is a further enlarged SEM photograph of FIG. 8;

FIG. 11 is a graph showing results obtained by analyzing a P1 area ofFIG. 10 using an EDAX (Energy-dispersive Analysis of X-rays) apparatus;

FIG. 12 is a graph showing results obtained by analyzing a P2 area ofFIG. 10 using an EDAX apparatus;

FIG. 13 is an exploded diagram of a circuit board according to anotherembodiment of the present invention;

FIG. 14 is a diagram schematically showing a structure of the circuitboard shown in FIG. 13;

FIG. 15 is a diagram showing one step for manufacturing a circuit boardaccording to one embodiment of the present invention;

FIG. 16 is a diagram showing a step after the step shown in FIG. 15;

FIG. 17 is a diagram showing a step after the step shown in FIG. 16;

FIG. 18 is a diagram showing a step after the step shown in FIG. 17;

FIG. 19 is a diagram showing a step after the step shown in FIG. 18;

FIG. 20 is a diagram showing a step after the step shown in FIG. 19;

FIG. 21 is a diagram showing a step after the step shown in FIG. 20; and

FIG. 22 is a sectional view schematically showing an electronic deviceaccording to one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Circuit Board

Referring to FIG. 1, there is shown a circuit board having a simpleconfiguration, but in practice, it has a more complicated configurationso as to satisfy functional and structural requirements depending on thetype of the circuit board. The illustrated circuit board has athree-dimensional circuit configuration composed of a substrate 1, acircuit pattern 2 and a through electrode 3. The substrate 1 may bevarious types of semiconductor substrates, a dielectric substrate, aninsulating substrate or a magnetic substrate. In the illustrateembodiment, the substrate 1 is a semiconductor substrate, e.g., asilicon wafer. In the case of a semiconductor substrate, an insulatingfilm is disposed on both sides and an interface between the throughelectrode 3 and the substrate 1. The insulating film may be a film of ametal oxide such as SiO₂ and Al₂O₃ and can be formed with a requiredthickness (depth) at a required location through a known chemicaltreatment.

The circuit pattern 2 is a thin-film disposed on at least one side ofthe substrate 1. In FIG. 1, another circuit pattern 4 is disposed on theother side of the substrate 1. The circuit pattern 2 may take variousplane patterns depending on the functional requirements. If necessary,the circuit pattern 2 may be surrounded by an insulating film. Thecircuit pattern 2 may be composed of a known material such as a metalmaterial containing a copper (Cu) as a main component. If necessary, itmay also contain indium (In), aluminum (Al) and bismuth (Bi). Thecircuit pattern 2 may be formed by using a thin-film formation techniquesuch as CVD or sputtering. These thin-film formation techniques are todeposit a thin-film under a vacuum atmosphere while heating.

The through electrode 3 is filled in a through-hole 30 extending fromone side of the substrate 1 in the thickness direction and having oneend connected to the circuit pattern 2. The through electrode 3 may becomposed of a metal material containing tin (Sn) as a main component andoptionally indium (In), aluminum (Al), bismuth (Bi), gallium (Ga) andantimony (Sb). In the case of containing bismuth (Bi), gallium (Ga) andantimony (Sb), it is possible to eliminate voids from the resultingthrough electrode 3 by using their cubical expansion properties. Ifnecessary, these materials of cubical expansion properties may becombined with noble metal components.

The through electrode 3 may further contain a magnetic component such asiron (Fe), cobalt (Co), nickel (Ni) and alloys thereof. With thesemagnetic components, there may be adopted a filling method using amagnetic force in a filling process for formation of the throughelectrode. If necessary, these magnetic components may be combined withnoble metal materials and the above materials of cubical expansionproperties.

Moreover, the through electrode 3 may contain a combination of at leastone kind of high melting metal particles selected from the groupconsisting of silver (Ag), copper (Cu), gold (Au), platinum (Pt),titanium (Ti), zinc (Zn), Aluminum (Al), iron (Fe), silicon (Si) andnickel (Ni) and at least one kind of low melting metal particlesselected from the group consisting of Tin (Sn), indium (In) and bismuth(Bi). This will be described later in detail.

In the illustrated embodiment, a single through electrode 3 is providedfor one circuit pattern 2, but it is also possible to provide aplurality of through electrodes 3 for one circuit pattern 2. Thethrough-hole 30 has a depth L and a diameter d1 at its bottom, wherein,preferably, the diameter d1 is 100 μm or less and an aspect ratio (L/d)is 1 or more, more preferably, the diameter d1 is 25 μm or less and theaspect ratio (Lid) is 5 or more. Such a through-hole 30 can be formed,for example, by laser piercing or chemical treatment. The through-hole30 is shaped to satisfy d2>d1, i.e., the diameter d2 at its upper openend is larger than the diameter d1 at its bottom.

The circuit pattern 2 and the through electrode 3 have dispersed areasAL1, AL2 containing a common noble metal component and are connected toeach other through the dispersed areas AL1, AL2. The noble metalcomponent is dispersed to have such a concentration gradient that itscontent (dispersed amount) is the highest at but decreases with distancefrom the interface between the dispersed areas AL1, AL2. In FIG. 1, thedispersed areas AL1, AL2 are defined by an alternate long and short dashline as if they were a defined area, but this is merely for purposes ofillustration. Actually, they don't have such a definite boundary.

Examples of noble metal include gold (Au), silver (Ag), platinum (Pt),palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru) and osmium(Os). Among them, the dispersed areas AL1, AL2 preferably contain atleast one component selected from the group consisting of gold (Au),silver (Ag), platinum (Pt), palladium (Pd) and alloys thereof.

With this configuration, the through electrode 3 can be connected to thecircuit pattern 2 without leaving any oxide film on the surface of thecircuit pattern 2. The circuit pattern 2, which has been formed under avacuum atmosphere with the above-described thin-film formationtechniques, is prevented from oxidizing during the film formationprocess, but exposed to the air during the process of forming thethrough-hole 30 and the through electrode 3, thereby oxidizing throughthe through-hole 30. However, even if an oxide film is produced on thesurface of the circuit pattern 2, as described above, the noble metalcomponent, for example, gold (Au) thermally diffuses into the metalcomponents constituting the circuit pattern 2, so that the oxide filmcan be reduced by catalysis of the noble metal. Accordingly, the throughelectrode 3 can be connected to the circuit pattern 2 without leavingany oxide film on the surface of the circuit pattern 2.

In addition, since the reduction of the oxide film, which is due to thecatalysis of the noble metal, does not need any flux, formation of voidsdue to a flux gas can be avoided.

The circuit board according to the present invention may be embodied invarious forms with respect to the through electrode structure. FIGS. 2to 5 illustrate such embodiments. In FIGS. 2 to 5, the portionscorresponding to those shown in FIG. 1 are indicated by the samereference symbols. It should be noted that as the materials constitutingthe through electrode, the above-mentioned noble metal materials,materials of cubical expansion properties and magnetic materials can beused, of course, but other materials may also be used withoutlimitation.

First referring to FIG. 2, the through-hole 30 satisfies d1>d2, where d1represents a diameter at the bottom and d2 represents a diameter at theupper open end. With this configuration, the through electrode 3 isprevented from coming out of the through-hole 30 toward the upper openend.

Next referring to FIG. 3, the through-hole 30 has a constriction at amid-portion, more specifically, at a height L1 from the bottom. Theconstriction has a diameter d3 that is smaller than the diameter d1 atthe bottom (i.e., d1>d3). This configuration also provides the sameeffects as that of FIG. 2.

The diameter of the through-hole 30 gradually increases upwardly at theportion having a height L2 (=L−L1) between the constriction of thediameter d3 and the upper open end, so that the upper open end has adiameter d2 that is larger than the diameter d3 (i.e., d2>d3). With thisconfiguration, since the molten metal and the like can be filled fromthe upper open end of a larger diameter d2 in the process of forming thethrough electrode, the filling process becomes easy. The diameter d2 maybe larger or smaller than the diameter d1 at the bottom.

Referring to FIG. 4, the through-hole 30 also has a constriction at amid-portion, more specifically, at a height L1 from the bottom. Theconstriction has a diameter d3 that is smaller than the diameter d1 atthe bottom (i.e., d1>d3), as in FIG. 3. However, the through-hole 30 ofFIG. 4 is different from that of FIG. 3 in that the upper portion fromthe constriction to the upper open end extends straight with a constantdiameter equal to the diameter d3.

Further referring to FIG. 5, the through-hole 30 has a roughened innerwall surface. The degree of roughness is preferably such that the ratioof a height h1 of the roughened surface, as measured from the bottom ofthe valley to the top of the hill, to the diameter d3 at the upper openend (i.e., h1/d3) falls within the range of 1/40 to 4/40.

In the embodiments of FIGS. 1 to 5, the through-hole 30 may be a roundhole, an elliptical hole, a square hole or a combination thereof, andmay have various diameters.

Next will be concretely described effects of the present invention withreference to experimental data shown in FIGS. 6 to 12 and in comparisonwith a conventional circuit board. The experimental data were obtainedfrom the embodiment of FIG. 1.

The circuit board shown in FIGS. 6 and 7 had a structure in which acircuit pattern 2 containing Cu as a main component was disposed on oneside of a silicon substrate 1 with one end of a through electrode 3directly connected to the circuit pattern 2. A flux was used forreducing an oxide film on the surface of the circuit pattern 2, and amolten electrode material containing molten Sn as a main component wasfilled into a through-hole 30 for formation of the through electrode 3.

As seen from FIGS. 6 and 7, considerably large voids were formed betweenthe periphery of the through electrode 3 and the inner wall surface ofthe through-hole 30. Although the flux reduction technique can reducethe oxide film on the surface of the circuit pattern 2, the flux filledinto the through-hole 30 along with the molten metal material generatesa flux gas. In circuit boards of this type, the through-hole 30 is amicropore having a diameter of, for example, several tens of μm and asignificantly high aspect ratio. Accordingly, if a flux gas is generatedin such a through-hole 30, the escape of gas inevitably becomesdifficult, forming voids due to the flux gas around the throughelectrode 3, which leads to a decrease in cross-sectional area of thethrough electrode 3, an increase in electrical resistance, poorconnection to the circuit pattern 2, and an increase in bond resistance.

In the circuit board according to the present invention, on the otherhand, the periphery of the through electrode 3 was in close contact withthe inner wall surface of the through-hole 30 formed in the substrate 1,leaving little voids therebetween, as shown in FIGS. 8 to 10. Although ashadow like a void can be seen between the circuit pattern 2 and thecontact surface of the through electrode 3, this shadow is not a voidbut a chip created by polishing when taking a SEM photograph.

Referring to FIG. 11 showing results obtained by analyzing a P1 area ofFIG. 10 using an EDAX apparatus, it is seen that the P1 area, which wasa center area of the through electrode 3, contained Sn as a maincomponent and also In, Cu and Bi.

Next referring to FIG. 12, it is seen that a P2 area, which was aportion of the through electrode 3 located close to the siliconsubstrate 1, further contained Au. With respect to Sn being a maincomponent of the through electrode 3, the row of SnL shows 17.42 wt. %and 3.29 at. %. With respect to Au, on the other hand, the row of AuLshows 1.24 wt. % and 0.14 at. %. As understood from this, Au wasdispersed in the through electrode 3 in a minute amount of 1.24 wt. %and 0.14 at. %.

When the through electrode 3 contains Bi, since the volume of Biincreases by about 3 to 3.5% upon solidification from the molten state,the voids, which would otherwise be formed between the inner wallsurface of the through-hole 30 and the through electrode 3 filled in thethrough-hole 30, can be eliminated by the cubical expansion of Bi.

When containing Sn, In, Cu and Bi, it has been confirmed that containing20 wt. % or more of Bi, 30 wt. % or less of In, 30 wt. % or less of Sn,and 1 to 5 wt. % of Cu is extremely effective in preventing theformation of voids.

The synergy between the void formation preventing effect due tocontaining Bi and the void formation preventing effect due to not usinga flux brings the through electrode 3 into close contact with the innersurface of the through-hole 30. Similar cubical expansion effects can beexpected from using gallium (Ga) or antimony (Sb) other than Bi.

FIGS. 13 and 14 show a multilayered circuit board having a multilayeredstructure of an arbitrary number of circuit boards A1 to A6, wherein atleast one layer may adopt the structure having the circuit pattern 2 andthe through electrode 3.

In the illustrated embodiment, each of the circuit boards A1 to A6adopts the structure having the substrate 1 with the circuit pattern 2and the through electrode 3. The circuit pattern 2 is formed on one sideof each of the circuit boards A1 to A6. Some of the circuit patterns 2extend over a few adjacent through electrodes 3.

The circuit boards A1 to A6 are bonded to one another at theirinterfaces through an adhesive. In the drawings, all the throughelectrodes 3 are connected to one another between the circuit boards A1to A6, but may not be connected to one another depending on the circuitconfiguration. In addition, the outermost circuit boards A1 and A6 areprovided with bumps (output electrodes) 60 to 69 as necessary. Themultilayered structure shown in FIGS. 13 and 14 is suitable forrealizing a circuit board of a complicated three-dimensional circuitconfiguration.

(Manufacturing Method)

Next will be described a method for manufacturing a circuit boardaccording to the present invention with reference to FIGS. 15 to 21.First of all, there is prepared a substrate 1 (wafer) with a circuitpattern 2 formed on one side, as shown in FIG. 15. The circuit pattern 2may be formed by adopting a thin-film formation technique such as CVD orsputtering.

Then, a resist 5 is applied to the other side of the substrate 1, asshown in FIG. 16, and then, a known photolithography process isperformed to form a resist mask 51 that has an opening of a diameter d2,as shown in FIG. 17.

Subsequently, a through-hole 30 is formed within the opening of theresist mask 51, for example, by using a laser irradiation or a chemicalreaction etching method, as shown in FIG. 18. The through-hole 30 isformed such that the surface of the circuit pattern 2 is exposed at thebottom of a diameter d1.

Subsequently, metal particles 4, at least the surface of which iscovered with a noble metal, are supplied into the through-hole 30 usinga screen printing method or the like, as shown in FIG. 19. In the screenprinting process, the screen printing may be performed while applying anultrasonic vibration to the substrate 1 or a squeegee (not shown).

The metal particles 4 may be entirely composed of a noble metal or mayhave a core of Sn or the like whose surface is covered with a noblemetal. For the metal particles 4, magnetic particles may also be used asa core whose surface is covered with a noble metal. In this case, themagnetic particles may have a grain size of 1 μm or less and be composedof at least one component selected from the group consisting of iron(Fe), cobalt (Co), nickel (Ni) and alloys thereof.

Moreover, the metal particles 4 may be nanoparticles so as to utilizethe melting point lowering effect due to a nano size. For example, themetal particles 4 may be supplied in such a minute amount as to formonly about one to three layers of metal particles on the surface of thecircuit pattern 2.

Subsequently, a molten metal material is filled into the through-hole 30to form a through electrode 3, as shown in FIG. 20. In this process, thecircuit board is placed under a vacuum atmosphere within a vacuumchamber and the molten metal material is filled into the through-hole 30through the pressure of the molten flow, while applying an ultrasonicvibration F1 to the substrate 1 (wafer). When filling the metalmaterial, powder is melted on the circuit board 1 and impregnated intothe micropores through the flow velocity, melting and vibration. Then,differential-pressure filling is performed by reducing the vacuum degreeof the vacuum atmosphere or changing the vacuum atmosphere to a normalatmosphere. Also in the differential-pressure filling, an ultrasonicvibration is applied. The fluid pressure can be controlled by adjustingthe operation of a rotating screw or a pump.

Instead of the differential-pressure filling, there may be adoptedcentrifugal filling which utilizes a centrifugal force during a rotationof the substrate 1 for filling of the molten metal material. Also in thecentrifugal filling, an ultrasonic vibration is applied as in thedifferential-pressure filling.

As has been described hereinabove, the molten metal material may containat least one component selected from the group consisting of bismuth(Bi), gallium (Ga) and antimony (Sb) and may optionally be combined withthe above-mentioned noble metal components.

The molten metal material may further contain Fe, Co, Ni and alloysthereof. In this case, instead of the differential-pressure filling,there may be adopted magnetic filling which applies an external magneticfield to the substrate 1 and utilizes its magnetic force to facilitatefilling of the molten metal material. Also in the magnetic filling, anultrasonic vibration is applied as in the differential-pressure fillingand centrifugal filling. As has been described hereinabove, ifnecessary, the magnetic components may be combined with the noble metalcomponents and the materials of cubical expansion properties. Since themagnetic components have a higher melting point than other componentsconstituting the molten metal material such as Sn, they can remain solidin the shape of particles within the molten metal material. The grainsize of the magnetic components is preferably 1 μm or less.

In the molten metal filling process, the noble metal component, forexample, gold (Au) can be alloyed by receiving a melting heat energy andthermally diffusing into the metal components constituting the circuitpattern 2. At this time, an oxide film formed on the surface of thecircuit pattern 2 can be reduced by catalysis of the noble metal.Accordingly, the through electrode 3 can be connected to the circuitpattern 2 without leaving any oxide film on the surface of the circuitpattern 2.

In addition, since the reduction of the oxide film, which is due to thecatalysis of the noble metal, does not need any flux, formation of voidsdue to a flux gas can be avoided. Similar effects can be obtained byusing Ag, Pt or Pd instead of Au.

Moreover, unlike the process of forming a thin-film of a finemultilayered structure using a photolithography process and a thin-filmformation technique, it is not technically difficult and does notrequire heavy investment in facilities to adopt differential-pressurefilling, centrifugal filling or magnetic filling in combination withapplying an ultrasonic vibration to the substrate 1 (wafer) for fillingthe molten metal material into the through-hole 30. This enables costreduction.

The molten metal material to be filled preferably contains high meltingmetal particles and low melting metal particles. The high melting metalparticles may contain at least one component selected from the groupconsisting of Ag, Cu, Au, Pt, Ti, Zn, Al, Fe, Si and Ni. The low meltingmetal particles may have a composite structure and contain at least onecomponent selected from the group consisting of Sn, In and Bi. Thecomposite structure refers to a composite containing at least one ofsingle crystal, polycrystal and amorphous. Preferably, the compositecontains polycrystal and single crystal.

The advantage of using the molten metal material containing the highmelting metal particles and the low melting metal particles is thatalthough the metal material contains the high melting metal particles,thermal melting upon filling can be performed at a temperature higherthan the melting point of the low melting metal particles but lower thanthe melting point of the high melting metal particles. Such alow-temperature heat treatment melts only the low melting metalparticles. This provides a filling structure in which voids between thehigh melting metal particles are filled up with the molten low meltingmetal particles, so that intermetallic bond dramatically improvesconductivity.

When Ag is used as the high melting metal particles, migration of Ag canbe reliably prevented because the surface of Ag is covered with the lowmelting metal particles.

When Cu is used as the high melting metal particles, oxidation of Cu canbe prevented because Cu is covered with the molten low melting metalparticles, as in the case of Ag.

The low melting metal particles have a composite structure. When the lowmelting metal particles having a composite structure are used for aconductive pattern, different crystal structures can coexist in a moltenstate without mixing with each other, thereby preventing disconnectiondue to a crack.

Preferably, the ratio of the high melting metal particles to the wholequantity of the conductive particles is 50 to 80 wt. %, while the ratioof the low melting metal particles to the whole quantity of theconductive particles is 20 to 50 wt. %. If the ratio of the high meltingmetal particles to the whole quantity of the conductive particles isless than 50 wt. %, their high conductivity cannot contribute to thewhole conductive composition. If the ratio of the high melting metalparticles to the whole quantity of the conductive particles is more than80 wt. %, on the other hand, since the amount of the low melting metalparticles is insufficient, the high melting metal particles may remainuncovered with the low melting metal particles and voids may be formedin the conductive layer, easily causing the problems of Ag migration andbeing unable to prevent oxidation of Cu.

Preferably, the high melting metal particles have a grain size of lessthan 20 nm. If the high melting metal particles have such a minute grainsize, they can be filled into a through-hole of a small diameter.

(Electronic Device)

Examples of electronic device according to the present invention includealmost everything that uses an electronic circuit as a functionalelement, such as a sensor module, an optoelectronic module, a unipolartransistor, a MOS-FET, a CMOS-FET, a memory cell, a FC (FieldComplementary) chip, integrated circuit, components thereof, and variousscales of LSIs.

Particularly, an integrated circuit adopting a circuit board accordingto the present invention as an interposer is appropriate as a typicalexample. As used herein, the integrated circuit includes a small-scaleintegration, a medium-scale integration, a large-scale integration, avery-large-scale integration (VLSI), and an ultralarge-scale integration(ULSI).

Referring to FIG. 22, a first integrated circuit LSI1 as a circuitfunctional part is mounted on one side of a first interposer InT1adopting circuit boards according to the present invention, a secondinterposer InT2 adopting circuit boards according to the presentinvention is mounted on one side of the first integrated circuit LSI1,and a second integrated circuit LSI2 is mounted on one side of thesecond interposer InT2.

Although FIG. 22 shows only the first and second interposers InT1, InT2,the number, internal wiring, thickness and shape of the interposers arearbitrary. This is also true for the first and second integratedcircuits LSI1, LSI2.

Signals from the first integrated circuit LSI1 to the second integratedcircuit LSI2 are transmitted to the second interposer InT2 throughconnections called “bump”. Inside the second interposer InT2, thesignals are transmitted to target bumps 65 to 69 through the internalwiring 2, 3 and then to the second integrated circuit LSI2 through thebumps 65 to 69. The signal transmission to the underlying firstintegrated circuit LSI1 can be performed in a similar way.

As shown in FIG. 22, the circuit boards according to the presentinvention are formed into the first and second interposers InT1, InT2and then combined with the first and second integrated circuits LSI1,LSI2 into a single chip. This realizes chip size package of electroniccircuits being the heart of IT devices and high-speed signaltransmission between the first and second integrated circuits LSI1,LSI2.

In addition, the second interposer InT2 disposed between the first andsecond integrated circuits LSI1, LSI2 enables signals to be transmittedat a high density and a high speed.

In recent CPUs, integrated circuits have an internal clock as high as afew GHz but the clock for transmitting signals to the outside of a chipis only a few hundred MHz, which causes the problem of wiring delay.With the circuit boards according to the present invention being used asthe first and second interposers InT1, InT2, however, the wiring lengthcan be minimized to solve the problems due to wiring delay.

Moreover, a delay in a buffer circuit for transmitting signals to theoutside and power consumption for driving cannot be ignored. With thecircuit boards according to the present invention being used as thefirst and second interposers InT1, InT2, however, the power consumptioncan be reduced.

Furthermore, ultraslim, powerful microcomputer systems can be realizedby stacking a CPU, a cache/main memory, an IO chip and the like on asingle chip.

In FIG. 22, the circuit boards according to the present invention areprovided as an independent component from the first and secondintegrated circuits LSI1, LSI2, but the present invention is alsoapplicable to the internal structure of the first and second integratedcircuits LSI1, LSI2, particularly to the local wiring. The presentinvention is also applicable to the internal wiring structure of notonly an active circuit element but also a passive circuit element.

While the present invention has been particularly shown and describedwith reference to embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit, scope and teaching of theinvention.

1. A circuit board comprising: a substrate; a circuit pattern; a throughelectrode; and a dispersed area, wherein said circuit pattern isdisposed on one side of said substrate in a thickness direction thereof,said through electrode is filled in a through-hole formed in saidsubstrate with one end connected to said circuit pattern, and saiddispersed area is an area in which said circuit pattern and said throughelectrode are connected to each other by dispersion and alloying of adispersed metal component, and said dispersed metal component isdispersed to have such a concentration gradient that its dispersedamount is the highest at but decreases with distance from an interfacebetween said circuit pattern and said through electrode, and saidthrough electrode comprises high melting metal particles and low meltingmetal particles, and intermettalic bond is formed between said highmelting metal particles and low metal particles, said high melting metalparticles contain at least one component selected from the groupconsisting of Ag, Cu, Au, Pt, Ti, Zn, Al, Fe, Si and Ni, and the lowmelting metal particles have a composite structure and contain at leastone component selected from the group consisting of Sn, In, and Bi. 2.The circuit board of claim 1, wherein said dispersed metal componentcontains noble metal component.
 3. A circuit board of claim 1, wherein athrough-hole for said through electrode satisfies d1>d2, where d1represents a diameter at a bottom thereof and d2 represents a diameterat an upper open end thereof.
 4. A circuit board of claim 1, wherein athrough-hole for said through electrode has at least one constrictionwith a reduced diameter at a mid-portion thereof in a height direction.5. The circuit board of claim 4, wherein said through-hole has adiameter which gradually increases from said constriction to said upperopen end.
 6. The circuit board of claim 4, wherein said through-hole hasa diameter which is constant between said constriction to said upperopen end.
 7. A circuit board of claim 1, wherein a through-hole for saidthrough electrode has a roughened inner wall surface.
 8. A circuit boardof claim 1, wherein a through-hole for said through electrode is a roundhole, an elliptical hole, a square hole or a combination thereof.
 9. Anelectronic device comprising: a circuit board; and a circuit functionalpart, wherein said circuit board is claimed in claim 1, and said circuitfunctional part is combined with said circuit board.